Television receiver



Feb. 14, 1939. K scHLESlNGER 2,147,554

TELEVI S ION RECEIVER Original Filed Jan. 21, 1935 to 1/2: lnaerm edl'ale I'reyaency am /1Y1 er Jame/7X00".

Patented Feb. 14, 1939 PATENT OFFICE TELEVISION RECEIVER Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Original application January 21, 1935, Serial No. 2,631. Divided and this application October 22, 1935, Serial No. 46,125. In Germany January 25, 1934 4 Claims. (01. 250- 20) This invention relatesto a radio receiving system of the heterodyne type and more particularly to a resonant input circuit coupled to the first detector stage having means to prevent the radiation of locally generated oscillations during reception of ultra-short waves.

This application is a division of my co-pending application Ser. No. 2,631, filed January 21, 1935.

The invention is directed to a new aerial connection arrangement for coupling a special aerial system with a heterodyne receiver using a valve which at the same time serves as a detector, oscillator and mixer, the oscillatory circuit of which is connected to anode and grid, whereby a capaci- 3-5 tive feed-back is effected only by the natural gridanode and grid-cathode capacities. The invention will be clearly understood by way of example shown in the accompanying drawing, in which- I Fig. 1 shows an embodiment of the aerial circuit coupled with the first stage of a heterodyne receiver in accordance with the invention,

Fig. 1a shows an aerial resonating at a quarter wave length which may be connected to the input 25 terminal 9 instead of the aerial circuit 38 shown in Fig. 1. a

It has been found to be extremely advantageous upon the reception of ultra-short waves to employ resonance aerials. The same may be 30 erected in the immediate vicinity of the receiving apparatus when the metal base of the receiver (see drawing) may be employed as electrical counterpoise. The coupling then takes place according to the invention as current coupling with the use of an aerial resonating at a quarter wave-length.

In other cases of reception which are important in practice it is necessary to select the point of erection of the aerial in spatial disposal amounting to a few wave-lengths from the point of erection of the receiving apparatus; for example, the aerial must be located on the roof of a building and the television receiver on the ground floor.

In Fig. 1 there is provided an aerial resonating at a half wave-length.

This aerial 3 in a manner known per se is connected in such fashion with an energy line 4 that at two points 5 and 6 disposed symmetrically to the potential anode of the aerial 3 the two poles of the energy line 4 are tapped and spaced in such fashion in relation to each other that the apparent resistance of the dipole existing between the same is equal to the wave resistance of the line 4, i. e., approximately 500 ohms. In this case advancing waves develop in the line, and as the applicant has established in practice, the

ultra-short wave may be transmittedover distances of the order of 20 metres and more without appreciable loss.

The coupling of the energy line at the receiver end may be performed by means of a step-up transformer with coils I and 8. These coils are preferably coupled very loosely with each other, and the coil 8 is adjusted with the inherent capacities, which arise from the aerial connection 9 to approximate resonance with the received wave. By reason of the loose coupling between I and 8 innumerable high damping effects areavoided, with consequent weakening of the resonance eiiect at 8 due to attenuation by the low-ohmic energy line 4 and the circuit of the coil 8. In practice, for example, the coil 1 possesses approximately 5 turns of mm. diameter, and the coil 8, with the dimensioning of the heterodyne circuit as set forth later, the same number of windings with half the diameter, and these two cylinder coils are arranged end to end, and the middle of the coil I may also be earthed in direct fashion. It is desirable to fit this transformer structure mechanically in the transmission line, in order to make the connection independent of adjustment on the part of the user.

Particular attention is paid to the elimination of a radiating effect of the locally produced heterodyne oscillation by the aerial. In connection with ultra-short wave reception this problem requires particularly serious consideration in practice, as particularly when using resonance aerials a large amount of radiation may be obtained if a decoupling between aerial and local oscillator is not effected. To avoid interferences of this character between two adjacent receivers the oscillatory heterodyne circuit l I, l2 oscillates with its two poles in push-pull in relation to the potential of cathode-earth. This is accomplished by a three-point connection system of the kind known per se, the requisite distribution of potential is produced by the inner capacities of the tube, and not by external couplings, such as backcoupling coils. The occurrence of interfering oscillations external to the oscillator is avoided by the difierential condenser I4, I5. The oscillatory circuit ll, l2 oscillates when the anode feed line I3 is not, as shown, tapped at the centre of the coil II, but is applied to the end thereof. The middle tapping as shown, however, as already known, provides a maximum oscillation amplitude. By means of the differential condenser I4, [5 a point is found which is neutral against earth potentials of any kind at the heterodyne frequency. This adjustment is performed in the first instance by the makers so that the aerial connection point 9 is then completely decoupled from the heterodyne oscillation of the tube I0, and radiation is avoided. The reception is passed through the medium of a parallel connection of the part capacities [4, I5 of the differential in phase to grid and anode of the tube I0, whereby no potential of the received frequency is produced at the terminals of the circuit I I, 12. The simultaneous connection in phase to grid and anode causes a weakening of the anode current amplified by the grid. The use of screening grid tubes, which overcome the anode reaction, results in a valuable improvement as compared with the use of single-grid tubes as oscillators [0. The point 9, therefore, viewed from the aerial, possesses against earth the nature of a capacity, the resulting amount of which is defined by the series connection of the parallel capacity of [4, l5 and the inherent capacities of the tubes and their circuits. A relatively small differential condenser 15 of approximately cm. part ca pacity, is used so that there is maintained a relatively large wave range in respect of the cir-' cuit l I, I2 with a decrease of detrimental longwave coupling, and also a favourable L/C' ratio for external resonance transformers 8.

For the purpose of precluding interfering long wave transmitters, for example in respect of those frequencies which fall within the order of magnitude of the relatively long intermediate frequency wave of the receiver (approximately 150-200 metres) employed, there are employed high-pass filters in the form 16, I1, which allow the passage of merely the ultra-short waves (for example capacity of 16-100 cm., and a coil of 17-30 windings, turns with 10 mm. diameter).

The long-wave absorption is additionally assisted by short circuiting the grid circuit of the tube I0 in respect of long waves by an ultra-short wave choke l8,'which is situated behind a small grid condenser 19 (50 cm.). Alternatively the two-section high-pass filter as described may also be applied in the aerial circuit or in the lead to the grid or the alternatively ultra-short wave resonance circuits may be connected in the manner of the transformer 1, 8. For economical operation on the part of the tube It! a negative bias of the control grid is important. This is effected in the most simple fashion by utilising the grid current at a grid resistance 20. In this manner there is also obtained simultaneously a constancy of the oscillation amplitude by self-regulation. By means of a blocking condenser 2| long waves, in accordance with the invention, are

completely earthed (approximately .1 mi).

The circuit elements 22, 23, and 25-21 in the anode circuit of the valve ID, are used for transmitting the intermediate frequency carrier with the corresponding side-bands intermediate frequency to the succeeding amplifier stages. 24 is a resistance in the anode supply line.

I claim:

1. In an ultra-short wave heterodyne receiver for wireless television an aerial circuit, a first stage used as local oscillator, amplifier and first detector stage, means ,for coupling said aerial circuit to said first stage, means for preventing radiation of oscillations of said local oscillator, said aerial circuit consisting of a resonance aerial, the length of which being one quarter or a multiple of one quarter of the received Wave-length, and being coupled to said first stage by means of a high-frequency transformer having a primary and a secondary, said primary being disecondary coils being arranged as to form a mechanically unvariable structure which is connected with the aerial circuit.

2. In an ultra-short wave heterodyne receiver for wireless television an aerial circuit, a first stage used as local oscillator, amplifier and first detector stage, means for coupling said aerial circuit to said first stage, means for preventing radiation of oscillations of said local oscillator, said aerial circuit consisting of a resonance aerial, the length of which being one quarter or a multiple of one quartw of the received wave-length, and being coupled to said first stage by means of a high-frequency transformer having a primary and a secondary, said primary being directly connected to said aerial, said secondary being connected to the grid and oscillatory circuit of said first stage by means of a differential condenser, said primary and secondary being coupled very loosely with each other and said secondary being dimensioned in combination with its inherent capacities to approximate resonance with the received wave, said differential condenser consisting of a rotary electrode and two fixed electrodes, said rotary electrode being connected to the input terminal which is connected through a high-pass filter to one terminal of the secondary the other one of which is earthed, said fixed electrodes being connected to the terminals of the oscillatory circuit which are connected at the one side to the anode of the first stage and at the other side via a capacity to the grid of said first stage, said grid being earthed via a grid leak resistance to which a capacity for the long-wave oscillations is connected in parallel.

3. In an ultra-short wave heterodyne receiver for wireless television an aerial circuit, a first stage used as local oscillator, amplifier and first detector stage, means for coupling said aerial circuit to said first stage, means for preventing radiation of oscillations of said local oscillator, said aerial circuit consisting of a resonance aerial, the length of which being one quarter or a multiple of one quarter of the received wave-length, and being coupled to said first stage by means of a high-frequency transformer having a primary and a secondary, said primary being directly connected to said aerial, said secondary being connected to' the grid and oscillatory circuit of said first stage by means of a differential condenser, said primary and secondary being coupled very loosely with each other and said secondary being dimensioned in combination with its inherent capacities to approximate resonance with the received wave, said differential condenser consisting of a rotary electrode and two fixed electrodes, said rotary electrode being connected to the input terminal which is connected through a high-pass filter to one terminal of the secondary the other one of which is earthed, said fixed electrodes being connected to the terminals of the oscillatory circuit which are connected at the one side to the anode of the first stage and at the other side via a capacity to the grid of said first stage, said grid being earthed via a grid leak resistance to which a capacity for the long-wave oscillations is connected in parallel, and an ultra-short wave choke.

4. In an ultra-short wave heterodyne receiver for wireless television an aerial circuit, a first stage consisting of a valve having an anode, a cathode, a control grid and a screening grid used as local oscillator, amplifier and first detector stage, means for coupling said aerial circuit to said first stage, means for preventing radiation of oscillations of said local oscillator, said aerial circuit consisting of a resonance aerial, the length of which being one quarter or a multiple of one quarter of the received wave-length, and being coupled to said first stage by means of a highfrequency transformer having a primary and a secondary, said primary being directly connected to said aerial, said secondary being connected to the grid and oscillatory circuit of said first stage by means of a difierential condenser, said primary and secondary being coupled very loosely with each other and said secondary being dimensioned in combination with its inherent capacities to approximate resonance with the received wave, said primary and said secondary coils being arranged as to form a mechanically unvariable structure which is connected with the aerial circuit.

KURT SCHLESINGER. 

